Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as available cellular telephone technology has increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
In the earliest cellular devices, the device included a numeric keyboard and small display for operation of the device. As cellular devices packaged more functionality therein, the typical numeric keypad gave way to the alphanumeric keypad, thereby allowing a user to readily enter full linguistic text. Another consequence of the expansion of cellular device functionality is the desire to increase display size and resolution. A typical tradeoff during design of cellular devices is the exchange of space between the display and the keypad. This design tradeoff may be more problematic as users demand smaller devices that are easier and more convenient to carry.
An approach to this design tradeoff is to include a touch screen input in the cellular device. In other words, this approach leans the aforementioned design tradeoff greatly in favor of the display by removing the keypad entirely as an input device, thereby providing the user with a larger display. Nevertheless, a potential drawback to these touch screen cellular devices is the lack of tactile feedback during input. Another approach is to include a touchless input device in the cellular device. For example, the cellular device may include a front facing camera which monitors the movement of the user's hand, thereby permitting touchless input. A drawback to this approach is that it is computationally intensive, which may be undesirable on a cellular device with limited battery power. Moreover, this approach may be subject to interference from backlight.